The present invention relates to an image display apparatus, which displays an image by using an electron emission element placed in matrix form, and a phosphor.
A matrix electron-emitter display is a display, wherein intersections of a group of electrodes mutually perpendicular are defined as pixels; an electron emission element is set on each of the pixels; the amount of emitted electrons are controlled by adjusting an applied voltage or a pulse width to every electron emission element; the emitted electrons are bombarded onto a phosphor after being accelerated in vacuum; light is emitted from a bombarded part of the phosphor. The electron emission element includes an element that uses a field-emission type cathode, an element that uses a MIM (Metal-Insulation-Metal) cathode, an element that uses a carbon-nanotube cathode, an element that uses a diamond cathode, an element that uses a surface-conduction electron-emitter element, an element that uses a ballistic electron surface-emitting cathode, and the like. Thus, a matrix electron-emitter display means a cathodoluminescent flat-panel display combining an electron emission element and a phosphor.
As shown in FIG. 8, a matrix electron-emitter display has a structure in which a cathode plate 601 placed with an electron emission element and a phosphor plate 602 forming a phosphor, are placed opposite. In order to make electrons emitted from an electron-emitter element 301 reach the phosphor and to excite the phosphor for emitting light, the space surrounded by the cathode plate, the phosphor plate and a frame component 603 is kept vacuum. In order to withstand the atmospheric pressure, a spacer (a support) 60 is inserted between the cathode plate and the phosphor plate.
The phosphor plate 602 has an acceleration electrode 122 and high voltage ranging from approximately 3 KV to 10 KV is applied to the acceleration electrode 122. Electrons emitted from the electron-emitter element 301 are bombarded onto the phosphor to excite the phosphor to emit light, after being accelerated by the high voltage.
A matrix electron-emitter display has a structure in which a cathode plate placed with an electron emission element and a phosphor plate forming a phosphor, are placed opposite. In order to make electrons emitted from the electron-emitter element reach the phosphor and to excite the phosphor for emitting light, the space surrounded by the cathode plate, the phosphor plate and a frame component is kept vacuum. In order to withstand the atmospheric pressure, a spacer (a support) is inserted between the cathode plate and the phosphor plate.
The phosphor plate has an acceleration electrode and high voltage ranging from approximately 3 KV to 10 KV is applied to the acceleration electrode. Electrons emitted from the electron-emitter element are bombarded onto the phosphor to excite the phosphor for emitting light, after being accelerated by high voltage.
An electron emission element to be used for a matrix electron-emitter display includes a thin-film electron emitter. The thin-film electron emitter has a structure in which a top electrode, an electron acceleration layer, and a base electrode are stacked and includes a MIM (Metal-Insulation-Metal) cathode, a MOS (Metal-oxide Semiconductor) cathode, a ballistic electron surface-emitting cathode and the like. The MOS cathode which uses a stacked film comprising of a semiconductor and an insulator as an electron acceleration layer and is described, for example, in Japanese Journal of Applied Physics, Vol. 36, Part 2, No. 7B, pp. L939-L941 (1997). The ballistic electron surface-emitting cathode uses porous silicon as an electron acceleration layer and is described, for example, in Japanese Journal of Applied Physics, Vol. 34, Part 2, No. 6A, pp. L705-L707 (1995). The thin-film electron emitter emits electrons accelerated in the electron acceleration layer into vacuum.
FIG. 2 shows an energy-band diagram showing an operation principle of a thin-film electron emitter. base electrode 13, an electron acceleration layer 12, and a top electrode 11 are stacked and a condition in which positive voltage is applied to the top electrode 11 is illustrated. In the case of a MIM cathode, an insulator is used as the electron acceleration layer 12. An electric field is generated in the electron acceleration layer 12 by voltage applied between the top electrode and the base electrode. By this electric field, electrons flow into the electron acceleration layer 12 from the base electrode 13 due to a tunneling phenomenon. These electrons are accelerated by the electric field in the electron acceleration layer 12 and become hot electrons. While these hot electrons pass through the top electrode 11, a part of electrons lose energy because of inelastic scattering and the like. When the hot electrons reach an interface between the top electrode 11 and vacuum, electrons, which have larger kinetic energy than surface work function Φ, are emitted into vacuum 10. In the present specification, an electric current which flows between the base electrode 13 and the top electrode 11 is referred to as a diode current Jd, and an electric current which is emitted into vacuum, is referred to as an emission current Je.
Compared with a field-emission type cathode, a thin-film electron emitter has a characteristic suitable for a display apparatus such as having high resistance to surface contamination, being able to realize a high-resolution display apparatus because of small divergence of an emission electron beam, having a voltage circuit driver with low voltage due to a low operation voltage, and the like.
On the other hand, in the thin-film electron emitter, only some part of a driving current is emitted to vacuum (an emission current Je). Here, the driving current is a current flowing between the top electrode and the base electrode, and it is sometimes referred to as a diode current Jd as well. The ratio α (electron emission ratio α=Je/Jd) of the emission current Je to the diode current Jd is ranging just from 0.1% to several tens %. That is, in order to get the emission current Je, it is necessary to supply the driving current (diode current) being just Jd=Je/α to the thin-film electron emitter from the driving circuit.